Stuart Wareham, who was said to be the driving force behind the murder and boasted in a letter: 'There's one more paedo off the street.' Photograph: Dorset police/PA

Three men have been given life sentences for the murder of a convicted child rapist.

Geoffrey Reed, 57, was beaten to death in his ground floor flat in Bournemouth, Dorset, by half brothers Stuart and Lee Wareham and Benjamin Walter.

Mr Justice Griffith Williams told Stuart Wareham, 26, he would serve a minimum of 20 years behind bars as he was the driving force behind the killing.

The other two men were given minimum terms of 18 years each at Winchester crown court on Thursday for what the judge said was a "terrifying attack" on 7 June last year.

Frail Reed, who allowed the men to stay or visit his flat, suffered "enormous injuries" with fractures to his head, ribs and sternum and a broken neck, the trial was told.

After the murder Stuart Wareham boasted in a letter from prison: "There's one more paedo off the street so he can't prey on any more little kids."

During the four-week trial the jury heard that Stuart Wareham found paperwork showing Reed had served 10 years for four counts of rape of two vulnerable victims – one of them a child.

The prosecution said this was a motive in the murder and also that the men wanted Reed's benefits.

After the fatal attack, the trio put eight-stone Reed in a suitcase that the jury saw Stuart Wareham on CCTV carry one-handed out of the flat.

Stuart Wareham then asked his sister to drive him and Benjamin Walter, 22, to their grandmother's house in Lytchett Matravers – 13 miles away – and said there was a dead dog in the suitcase he wanted to bury there.

Meanwhile Lee Wareham, 33, left the house with several bags and dumped Reed's clothes while the other men buried him in a shallow grave.

Another man, Danny Anderson, was living in the flat and he called police three days later, fearing the men had killed Reed.

Specialist dogs found him buried in woodland. Each man blamed the others for the killing and each had shown no remorse for the murder, the court was told.